Despite a recent reduction in the number of human immunodeficiency virus (HIV) infections attributed to injecting drug use in the United States,1 9% of new U.S. HIV infections in 2009 occurred among injecting drug users (IDUs).2 To monitor HIV-associated behaviors and HIV prevalence among IDUs, CDC's National HIV Behavioral Surveillance System (NHBS) conducts interviews and HIV testing in selected metropolitan statistical areas (MSAs). This report summarizes data from 10,073 IDUs interviewed and tested in 20 MSAs in 2009. Of IDUs tested, 9% had a positive HIV test result, and 45% of those testing positive were unaware of their infection. Among the 9,565 IDUs with HIV negative or unknown HIV status before the survey, 69% reported having unprotected vaginal sex, 34% reported sharing syringes, and 23% reported having unprotected heterosexual anal sex during the 12 previous months. Although these risk behavior prevalences appear to warrant increased access to HIV testing and prevention services, for the previous 12-month period, only 49% of the IDUs at risk for acquiring HIV infection reported having been tested for HIV, and 19% reported participating in a behavioral intervention. Increased HIV prevention and testing efforts are needed to further reduce HIV infections among IDUs.

NHBS monitors HIV-associated behaviors and HIV prevalence among populations at high risk for acquiring HIV. In 2009, NHBS staff members in 20 MSAs with high prevalence of acquired immunodeficiency syndrome (AIDS)* collected cross-sectional behavioral risk data and conducted HIV testing among IDUs using respondent-driven sampling, a peer-referral sampling method.3,4 Recruitment chains in each city began with one to 15 initial participants recruited by NHBS staff members during formative assessment and planning. Initial participants who completed the interview were asked to recruit up to five other IDUs through use of a coded coupon system designed to track referrals. Recruitment continued for multiple waves; all participation was voluntary. Persons were eligible to participate if they had injected drugs during the previous 12 months, resided in the MSA, and could complete the interview in English or Spanish. After participants gave oral informed consent, in-person interviews were conducted by trained interviewers who administered a standardized, anonymous questionnaire about HIV-associated behaviors. All respondents were offered anonymous HIV testing, which was performed by collecting blood or oral specimens for either rapid testing in the field or laboratory-based testing. A nonreactive rapid test result was considered HIV negative; a reactive rapid test result was considered HIV positive if confirmed by Western blot or indirect immunofluorescence assay. Incentives were offered for participating in the interview, completing an HIV test, and for recruiting IDUs to participate.†

For this report, data on HIV testing and 13 HIV-associated behaviors were analyzed. Participants were asked whether, in the previous 12 months, they 1) had shared syringes; 2) had shared injection equipment other than syringes; 3) had vaginal sex; 4) had unprotected vaginal sex; 5) had heterosexual anal sex; 6) had unprotected heterosexual anal sex; 7) had male-male anal sex; 8) had unprotected male-male anal sex; 9) had more than one opposite sex partner; 10) had been tested previously for HIV infection; and 11) had participated in an HIV behavioral intervention. In addition, participants were asked whether they had ever been tested for 12) HIV or 13) hepatitis C virus (HCV) infection.§ IDUs who tested HIV positive during the survey were defined as unaware of their HIV infection if they had reported that their most recent previous HIV test result was negative, indeterminate, or unknown, or that they had never been tested. IDUs with self-reported negative, indeterminate, or unknown status (including those who tested positive during the survey), were considered to be at risk for acquiring HIV. Data from each MSA were analyzed using a respondent-driven sampling analysis tool that produces estimates adjusted for differences in peer recruitment patterns and size of participant IDU peer networks. Results from these analyses were aggregated and weighted by the size of the IDU population in each MSA5 to obtain estimates overall.¶

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In 2009, a total of 13,186 persons were recruited to participate; of these, 2,687 (20%) were found ineligible. An additional 426 (3%) eligible participants were excluded from analysis.** Data for the remaining 10,073 participants were used in the analysis of HIV prevalence and participant awareness of serostatus (Table 1). To focus the analysis of HIV-associated behaviors on persons at risk for acquiring HIV infection, 508 participants who reported that they previously had tested positive for HIV were excluded (Table 2).

Among 10,073 IDUs, 9% tested positive for HIV. Prevalence of HIV infection was higher among Hispanics (12%) and non-Hispanic blacks (11%) than non-Hispanic whites (6%). IDUs in the Northeast and South regions had higher HIV prevalence (12% and 11%) than those in the Midwest and West regions (5% and 6%). Those with less than a high school education had higher HIV prevalence (13%) than IDUs who completed high school (8%) or had more than high school education (7%) (Table 1). Among HIV-infected IDUs, 45% (95% confidence interval [CI] = 38%-51%) were unaware of their infection.

The prevalence of HIV-associated risk behaviors in the previous 12 months generally decreased with increasing age. For example, among persons aged 18-29 years, 52% reported sharing syringes, compared with 39% aged 30-39 years, 34% aged 40-49 years, and 25% aged ≥50 years. A higher percentage of IDUs with less than a high school education reported sharing syringes (38%), compared with high school graduates (32%) or those with higher education (31%). Lower percentages of IDUs with less than a high school education reported participation in HIV interventions (16%) and testing for HCV infection (67%), compared with those with a high school education (20% and 73%, respectively) and those with higher deducation (24% and 78%, respectively). A higher percentage of those living at or below the federal poverty level (35%) shared syringes than those above the poverty level (27%), and a lower percentage of those living at or below the poverty level had HCV testing (70%) than those above the poverty level (78%) (Table 2).

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